An engine may include one or more compression devices for each cylinder bank. The compression devices may enable increased engine performance by increasing an amount of air that may enter engine cylinders. In one example, a first compressor may supply a first amount of air to the engine and a second compressor may supply a second amount of air to the engine. The first amount of air may be equal to the second amount of air, or the first amount of air may be different from the second amount of air. If the first amount of air is different than the second amount of air, different pressure ratios may develop across the first and second compressors. As a result, it may be possible for air to flow backward through one of the compressors, thereby reducing compressor efficiency and engine air flow. While it may be possible to closed-loop control each of the two compressors so that the two compressors provide a substantially same amount of air to the engine, the closed-loop control may be difficult to apply and it may increase system cost more than is desired.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method for operating an engine, comprising: adjusting speed of a third compressor and a position of a valve in response to an engine air flow amount, the third compressor and the valve positioned in an air intake of an engine upstream of an engine throttle, the third compressor positioned in the air intake downstream of first and second compressors.
By adjusting speed of a third compressor and a position of a valve in an engine air intake, it may be possible to provide a desired air flow to an engine without inducing back flow through a compressor that has a lower pressure ratio than the third compressor and that is positioned in parallel with the third compressor. For example, at middle level engine air flow amounts, all air entering an engine may flow through the third compressor and air flow through a path in the engine intake that is in parallel with the third compressor may be ceased since the third compressor has capacity to meet the request boost and engine air flow. Consequently, air may not flow back through a fourth compressor located in the parallel path, thereby avoiding air back flow in the fourth compressor at middle level engine air flow amounts. As such, closed loop control of the third and fourth compressors at middle engine air flow amounts may be avoided. If the engine air flow amount is increased to a higher level, the valve may be opened so that the fourth compressor may further increase engine air flow, and since flow rates through both the third and fourth compressors is high, the possibility of backflow through one of the third and fourth compressors may be reduced.
The present description may provide several advantages. Specifically, the approach may simplify compressor control for an engine and improve system response. In addition, the approach may reduce system electrical consumption when the engine compressors are electrically driven. Further, the approach may be applied to systems where the compressors are mechanically driven or electrically driven.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.